Articulated dump trucks have a unique configuration that includes bin lift cylinders positioned such that it requires the force exerted by the cylinders to be much greater at the beginning than for the ensuing portion of an operation for dumping a loaded bin. Stated otherwise, the hydraulic pressure required by the cylinders to dump the load proportionally decreases as the bin is raised.
A known dump truck has a bin that is lifted to a maximum tipping angle of approximately seventy degrees from the horizontal during the bin dumping operation. When the bin of this known dump truck has been tipped an amount approximating 50% of the maximum tipping angle, the force required is roughly half the force the cylinder is required to provide to lift the bin at the beginning of the dumping operation.
Some dump truck designs use multi-stage lift cylinders to take advantage of the fact that decreasing force is required as lift increases. A multi-stage cylinder at initial extension provides high force at low speed. As the cylinder extension continues and the additional stages are activated, speed increases and force decreases. Thus, faster bin raise times are realized.
The problem with multi-stage cylinders is that they are more expensive and prone to leaks and other problems versus a single stage cylinder.
The problem to be solved then is how to efficiently utilize the operating pressure fluid that is routed to the lift cylinders during dumping a dump truck bin so as to minimize the amount of time it takes to dump a loaded dump truck bin without increasing the size of the pressure fluid supplying pump and the plumbing required beyond that used in systems using single stage cylinders, or to make it possible to decrease the size of the pump without sacrificing dump speed.